Phase inverter question...

[Greg_L]

Maybe this is a dumb question, I'm still learning.

Why is a phase inverter called a phase inverter and not a polarity inverter? Polarity is a shift in positive vs negative, whereas phase is more a time based phenomenon. A phase inverter makes two equal but opposite polarity signals, does it not?

Am I wrong here?

[g1]

Phase is more relative. Polarity is usually DC. If an AC signal was riding on DC it might never change polarity, but could reverse phase.

[Helmholtz]

You're absolutely right.
A phase inverter (aka phase splitter) provides 2 output signals having opposite polarity at each point in time.
The phase difference between output signals always is 180°, meaning a multiplication by -1.

I'd actually prefer the term "signal polarity inverter".

[Greg_L]

Phase is more relative. Polarity is usually DC. If an AC signal was riding on DC it might never change polarity, but could reverse phase.

But even still isn't it actually reversing polarity? What if the AC signal was riding on 0VDC? The reversed signal would be swinging positive and negative...but exactly reversed from the original, not through time, but through voltage.

I'm not trying to change 100 years of tube terminology. I'm just trying to get a better understanding.

[Greg_L]

You're absolutely right.
A phase inverter (aka phase splitter) provides 2 output signals having opposite polarity at each point in time.
The phase difference between output signals always is 180°, meaning a multiplication by -1.

Right that's how I understand it. They are exact opposite in polarity, but not phase because they are still in time with each other. They are a perfect mirror image which is a net of zero.

[Helmholtz]

... but not phase because they are still in time with each other. .

They are because sin (-x) = -sin (x), x being the phase. So phase reversal and polarity reversal mean the same.

[g1]

But even still isn't it actually reversing polarity? What if the AC signal was riding on 0VDC? The reversed signal would be swinging positive and negative...but exactly reversed from the original, not through time, but through voltage.

It's tricky terminology and I think maybe just to avoid confusion. It is reversing polarity with reference to itself. But AC voltage does not really have polarity so that is the confusion I think being avoided.
Same with balanced audio, the term 'opposite phase' is usually used rather than 'opposite polarity'. (even though they often use + and - to denote the phase. )

[Helmholtz]

It is reversing polarity with reference to itself. But AC voltage does not really have polarity so that is the confusion I think being avoided.

AC voltage has a well defined polarity at each point in time. Yes, it's constantly changing, but so is phase (rotating all the time, repeating itself after each full cycle of 360° like a clock.).
Polarity reversal is rather unambiguous.
It doesn't get any simpler using the term phase instead, which requires some familiarity with trigonometry.

I wonder how many technicians really know what phase means.

[g1]

I'm not saying phase is the better term here, just giving some background as to why the terminology may be what it is. If you look up 'AC polarity', it's a no-go.

[Helmholtz]

. If you look up 'AC polarity', it's a no-go.

Sorry, but that's stupid.
You have to discern between time averaged and momentary polarity.
Time average of a pure AC signal must be zero, so polarity is meaningless.

Just look at your scope (with AC coupling) and push the "invert" button.

I don't think polarity reversal with AC signal can be misinterpreted.
Multiplying by -1, phase reversal or polarity reversal all means the same in electronics.

I'm definitely with the OP here.

[Greg_L]

Sorry, but that's stupid.
You have to discern between time averaged and momentary polarity.
Just look at your scope (with AC coupling) and push the "invert" button.

I don't think polarity reversal with AC signal can be misinterpreted.
Multiplying by -1, phase reversal or polarity reversal all means the same in electronics.

I'm definitely with the OP here.

Ha don't be with me, I don't know jack squat!

Let me explain where this came from real quick....

A friend of mine shared with me some really bad, obviously A.I. written "articles", and one of them was about phase inverters.
This is hilarious, hold on to your seat...
https://www.fuelrocks.com/what-is-a-...er-guitar-amp/

Anyway, I was explaining in my own layman's way how a phase inverter works and what it does.
He countered with, "wouldn't that be more like a polarity inverter"?
And I was like, "Yeah, you know, I think so. They call it 'phase inverter' because that's just what it's always been called but it is really just flipping polarity on one of the split signals".
But I don't know for sure so I thought I'd run it by you more knowledgeable types.

[g1]

Sorry, but that's stupid.

I think you have a good enough understanding of english that you're just being belligerent now (to put it diplomatically). Have a nice day.

[Helmholtz]

Does AC voltage have a polarity?

Definitely!
No voltage without a polarity. Electrons need to know where to flow.
With ACV, polarity is changing with doubled frequency of the fundamental.
Time averages of ACV and polarity are zero, but what is the sense of time averaging ACV?
Averaged ACV would have no effect at all.

Now, what is the time average of phase?

[The Dude]

Of course it's purely semantics. I think most of us here understand conceptually what happens in a phase inverter circuit. SO, I don't mean to stir things up. My opinion is that AC "polarity" is referred to as phase, hence the term phase inverter. Sure AC has "polarity" when it's not right on the 0V line, but that's not how we generally refer to that phenomenon. It's why there is no polarity stated on a wall wart that uses an AC/transformer only adapter, and why it's necessary to state polarity for a DC wall wart. Again, it's terminology/semantics. The important thing is to understand how the circuit works. That's my $.02. You may now go back to your regularly scheduled argument.

[Helmholtz]

I think you have a good enough understanding of english that you're just being belligerent now (to put it diplomatically). Have a nice day.

Stupid referred to "no-go". I should have said "wrong" instead.